Gas stripping ethanol fermentation system

The method of product removal from fermentation medium to prevent product inhibition and to improve the productivity by applying gas stripping in the ethanol fermentation (GSEF) is investigated experimentally and analytically. In a GSEF system, the stripping effect was modeled by a quasi-steady-state assumption in the gas phase, using a newly defined "stripping factor". The effects of temperature and gas flow rate on the stripping factor were investigated in a batch ethanol-water system experimentally. The mass transfer effect was negligible in the experimental range investigated. The Henry's law constants are obtained from the stripping experiments for 35°C, 50°C and 60°C. They are to be used in the estimation of the ethanol removal rate associated with stripping factor in a GSEF system. Also, a simple strippercondenser experiment has shown effectively not only in product removal but also in product concentration in the overhead condenser. The advantages of the GSEF system are demonstrated by using a modification of Ghose and Tyagi growth kinetics (1979) together with Luedeking-Piret (1959) production model; namely, the cell concentration, productivity and substrate consumption increase with an increase in the stripping factor, and the ethanol concentration in the broth decreases with an increase in the stripping factor. The enhancement of productivity is mainly due to an increase in the cell concentration and to an increase in the substrate utilization in the system.